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The Bovidae are the most diverse group of living ungulates with 143 Recent
species (over 55% of modern ungulates). Bovids are primarily Old
World in their distribution, although a few species are found in North
America. The name "antelope" is often used to describe many members
of this family, but it is not a definable, taxonomically-based term
- if it's not an ox, goat, or sheep, then it's an antelope; antelope
are found in all eight modern bovid subfamilies alongside distinctly
non-antilopine species.
The present classification scheme for bovids recognizes eight subfamilies
subdivided into two clades, the Boodontia (with a single subfamily, Bovinae)
and Aegodontia (composed of all other bovid subfamilies). Some authors
do not recognize these two clades, instead reducing the number of subfamilies
to two: Bovinae (without change) and Antilopinae (with all of the Aegodontid
subfamilies as tribes within it). Among the eight subfamilies presented
here, the phylogeny of some groups is well-established (e.g., the Bovinae
are monophyletic and basal; the Caprinae, Hippotraginae, and Alcelaphinae
cluster together consistently), while the interrelationships of the other
subfamilies are still under question.
The family Bovidae began its evolution in Africa around 19 million years
ago, and rapidly diversified, with 78 genera known from the Miocene (compared
to 50 today). Kingdon (1997) suggests that a continental divide between
Africa and Eurasia may be responsible for the early divergence of the Boodontia
(Eurasian in origin) and the Aegodontia (which continued evolving in Africa).
The rejoining of the two continental land masses (after these two principal
clades had become distinct) at the Arabian peninsula removed this geographic
barrier, allowing both groups to expand into the other's homeland.
Today, Africa remains the heart of bovid diversity (representatives
of all eight modern families inhabit the continent, and four of
these families are found nowhere else). Three bovid subfamilies
(Bovinae, Caprinae, and Antilopinae) are well-represented in Eurasia (while
a fourth subfamily, the African Hippotraginae, has a single representative
on the Arabian peninsula). The Americas, in comparison, have very few
bovids (only five bovid species are native to the Nearctic region, and no
bovids are found in the Neotropics). The bovid invasion of North America
is relatively recent: the Bering Land Bridge connected Russia and Alaska
during the Pleistocene and its northern climate prevented all but the
most cold-tolerant species from crossing to North America.
One of the defining characteristics of this family is the presence of unbranched
horns. Horns are present in males of all bovid species and in females
of some genera (most frequently in large species where adult females weigh
over 40 kg). When horns are present in both sexes, those of males are always
thicker at the base and more complex. The horns are permanently attached
to the frontal bones of the skull, and are composed of a bone core covered
with a keratin sheath (which is never shed). An air space separates these
two layers, with the result that bovids are often called "hollow-horned
ungulates". Tetracerus is unique among wild bovids in that
males regularly bear four horns (two pairs); all other genera (with the exception
of some domestic sheep) have only one pair. Bovids have the typical
dentition of the ruminants - I 0/3, C 0/1, P 3/3, M 3/3 x 2 = 32. The
upper canines are always absent. A single lacrimal canal is usually
present in the orbits of the skull. |
